From the General Instruction of the Roman Missal (GIRM), for “Mass With a Deacon”:
“178. After the Universal Prayer, while the Priest remains at the chair, the Deacon prepares the altar, assisted by the acolyte, but it is the Deacon’s place to take care of the sacred vessels himself.”
For “Mass Without a Deacon” the GIRM has:
“139. When the Universal Prayer is over, all sit, and the Offertory Chant begins (cf. no. 74).
An acolyte or other lay minister places the corporal, the purificator, the chalice, the pall, and the Missal on the altar.”
Post #1 has: “I’m not speaking of altar servers, but a scenario where parishioners bring forward the gifts and then set-up the altar before the priest begins the consecration.”
Well, it seems they are doing part of the role of altar servers.
A clearly incorrect practice I often see, is the Priest setting up the altar, instead of a lay minister. Another incorrect practice is putting the corporal on the altar before the beginning of Mass.
Setting up the altar by those bringing forward the gifts is an improvement on this. If the parish priest believes he lacks parishioners with the enthusiasm to be altar servers, then I can understand him taking this approach.
If there were a Deacon, first he would set up the altar, while Priest is at the chair. Then the Priest would accept the gifts from the offertory procession, assisted by the Deacon. (GIRM 178). So, it would be better if the lay people set up the altar before the gifts were brought forward, not after the offertory procession.